In this thesis, we take a critical look at the evidential studies scholarship surrounding the forged Outer Book of the Mengzi (孟子外書). The received knowledge concerning this book is that it was forged during the late years of the Ming dynasty by a master forger Yao Shilin (姚士粦). After clearing up how the book was circulated, though, we find that this work didn’t become a subject of discussion until the middle of the Qianlong era of the Qing dynasty, more than a hundred years after the Ming had already fallen. A further look at the discussion surrounding this book then shows that much of the proof offered up to show that this book was a Ming-period forgery simply does not hold up. In the absence of any such evidence, we go on to consider evidence that this book could have been produced as early as the Song dynasty, perhaps by somebody close or familiar with Sima Guang (司馬光).